Weather ‘extremes off the scale’

And the United States is about to experience an extreme Christmas, according to forward forecasts.

Something very odd is happening to the jetstreams of air that circle the globe.

And it's about to generate another of the 'polar vortex' effects that has slammed the United States with heavy snow falls much further south than usual in recent years.

But mother nature demands balance.

Alaska will be sweltering. California is already embraced by midwinter wildfires.

"Also, because I know this isn't actually obvious, but the warmth over Alaska isn't occurring because the sun is burning bright in the daytime sky," says weather.us metrologist Ryan Maue. "(It's) advection. Relentless marine flow from Pacific piling up."

California has experienced one of its largest wildfires in history. Picture: Mike Eliason/Santa Barbara County Fire Department via AP

Essentially, strong currents of abnormally hot water are moving north towards Alaska out of the Pacific Ocean. This hot water in turn warms up the air, and it's expected to move over the Arctic ice cap itself - forcing the cold air that was there down towards the United States.

"On the 'drunk jet stream' or 'jet weirding' scale of climate disruption, the upcoming next 7-10 days will see extremes off the scale," Maue says.

Alaska and parts of Canada will experience Christmas temperatures some 10C above normal. "That is above freezing into the Arctic (on) Christmas Eve," he says.

Abnormally warm water is moving north towards Alaska. Picture: Supplied

Current weather models predict this will force a blast of frigid air to punch down over North America, through the mainland United States and into the Rocky Mountains with air some 10C cooler than normal.

"If you're West of the Mississippi River on Christmas Day, then you may want to ask for coal in your stocking," Maue says. "Extreme cold arriving via Polar Express. Off the charts Arctic cold."

Expectations are it will hit Denver, Colorado, particularly hard. Surface pressures are expected in the high 1040mb to 1060mb range.

"Now that would be a memorable trip to return your gifts on the day after Christmas in Denver," he says. "-30°F (-34C) showing up on the 10 day highlights potential for deadly cold - regardless of exact number, the bottom will drop out."